Method for non-contrast enhanced magnetic resonance angiography

Abstract

A method for non-contrast enhanced magnetic resonance angiography (“MRA”) that has a short scan time and is insensitive to patient motion is provided. More particularly, the method provides significant arterial conspicuity and substantial venous signal suppression. A two-dimensional single shot acquisition is employed and timed to occur a specific time period after the occurrence of an R-wave in a contemporaneously recorded electrocardiogram. In this manner, k-space data is acquired that is substantially insensitive to variations in arterial flow velocity, or heart rate, and that further substantially suppresses unwanted venous signal in a prescribed imaging slice.

The invention claimed is:  
     
       1. A method for non-contrast-enhanced magnetic resonance angiography to produce an image representative of the vasculature of a subject with a magnetic resonance imaging (MRI) system, the steps comprising:
 a) acquiring a signal indicative of a cardiac phase of the subject; 
 b) performing a pulse sequence that directs the MRI system to:
 i) apply at a time point determined based on the signal acquired in step a), a radio frequency (RF) saturation pulse to a prescribed imaging slice such that MR signals therein are suppressed; 
 ii) apply an RF saturation pulse to a prescribed slab that is outside of the imaging slice, such that MR signals indicative of venous blood that flows into the imaging slice are suppressed; 
 iii) wait a period of time during which no RF pulses are applied; 
 iv) acquire k-space data from the subject following the application of an RF excitation pulse; 
 wherein the period of time in step b)iii) begins at a time point at which the RF saturation pulse is applied in step b)ii) and lasts for a duration sufficient to allow spins associated with unsaturated arterial blood and spins associated with saturated venous blood to flow into the prescribed imaging slice at a time point at which k-space data is acquired in step b)iv); and 
 
 c) reconstructing, from the acquired k-space data, an image of the subject that is representative of the vasculature of a subject. 
 
     
     
       2. The method as recited in  claim 1  in which step b)iv) includes acquiring k-space data as a single shot in coordination with the application of a series of RF excitation pulses. 
     
     
       3. The method as recited in  claim 1  in which the signal indicative of a cardiac phase of the subject acquired in step a) is an electrocardiogram. 
     
     
       4. The method as recited in  claim 1  in which the period of time in step b)iii) occurs during rapid systolic inflow of arterial blood into the imaging slice. 
     
     
       5. The method as recited in  claim 4  in which the pulse sequence further directs the MRI system to wait another period of time before performing step b)i). 
     
     
       6. The method as recited in  claim 5  in which the another period of time and the period of time in step b)iii) are selected such that step b)iv) occurs during slow diastolic inflow of arterial blood into the imaging slice. 
     
     
       7. The method as recited in  claim 6  in which step b)iv) includes acquiring k-space data from a central portion of k-space before acquiring k-space data from a peripheral portion of k-space. 
     
     
       8. The method as recited in  claim 7  in which step b)iv) includes acquiring k-space data from a zero-line in k-space using zero phase-encoding before acquiring k-space data from the remainder of k-space. 
     
     
       9. The method as recited in  claim 5  in which the another period of time is between 0 and 150 milliseconds. 
     
     
       10. The method as recited in  claim 4  in which the period of time in step b)iii) is between 100 and 400 milliseconds. 
     
     
       11. The method as recited in  claim 1  in which the period of time in step b)iii) is selected such that step b)iv) occurs during slow diastolic inflow of arterial blood into the imaging slice. 
     
     
       12. The method as recited in  claim 11  in which step b)iv) includes acquiring k-space data from a zero-line in k-space using zero phase-encoding before acquiring k-space data from the remainder of k-space. 
     
     
       13. The method as recited in  claim 1  in which step b)iv) includes acquiring k-space data from a central portion of k-space before acquiring k-space data from a peripheral portion of k-space. 
     
     
       14. A method for non-contrast enhanced magnetic resonance angiography with a magnetic resonance imaging (MRI) system, the steps comprising:
 a) acquiring an electrocardiograph (ECG) signal from a subject; 
 b) applying a radio frequency (RF) saturation pulse to a prescribed imaging slice in the subject and at a preselected time after the occurrence of an R-wave in the acquired ECG signal in order to suppress MR signals in the imaging slice; 
 c) applying an RF saturation pulse to a prescribed slab that is outside of the imaging slice in order to suppress MR signals from venous blood that flows into the imaging slice; 
 d) waiting a preselected period of time during which no RF pulses are applied to the subject, the preselected period of time having a duration sufficient to allow spins associated with unsaturated arterial blood and spins associated with saturated venous blood to maximally flow into the prescribed imaging slice at a time point at which k-space data will be acquired; 
 e) applying an RF excitation pulse to the subject after the preselected period of time has elapsed; 
 f) acquiring k-space data from the subject following the application of the RF excitation pulse; and 
 g) reconstructing, from the acquired k-space data, an image of the subject. 
 
     
     
       15. The method as recited in  claim 14  in which the preselected period of time in step d) occurs during rapid systolic inflow of arterial blood into the imaging slice. 
     
     
       16. The method as recited in  claim 15  in which the preselected period of time in step d) is selected such that step f) occurs during slow diastolic inflow of arterial blood into the imaging slice. 
     
     
       17. The method as recited in  claim 16  in which step f) includes acquiring k-space data from a central portion of k-space before acquiring k-space data from a peripheral portion of k-space. 
     
     
       18. The method as recited in  claim 17  in which step f) includes acquiring k-space data from a zero-line in k-space using zero phase-encoding before acquiring k-space data from the remainder of k-space. 
     
     
       19. The method as recited in  claim 17  in which the preselected period of time in step d) is between 100 and 400 milliseconds. 
     
     
       20. The method as recited in  claim 17  in which the preselected time in step b) is 100 milliseconds. 
     
     
       21. The method as recited in  claim 14  wherein the RF saturation pulse has a flip angle of 90 degrees.